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Thread: Radford System

  1. #11
    Join Date: Sep 2014

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    I'm John.

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    Have a look at this Barry, solid state rectification for IMA series but I’m pretty sure these are K25 amps. You can just see the XLR input in the EBay photographs. It seems the K25 were a modified MA-25 for the BBC specifically for use with the KEF LS5/1A monitors. They amps have a filter for evening out the speaker’s frequency response but this can be switched out. They also have input trim pots but no impedance selector switch.




  2. #12
    Join Date: Sep 2014

    Location: Northern Ireland

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    I'm John.


  3. #13
    Join Date: Jan 2009

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    I'm openingabottleofwine.

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    Oh - this is embarrassing!

    The table you show is exactly the same as the one shown in our article, there is thus no excuse for me not knowing about it. So definitely a K25, which if the frequency equalisation can be switched out, makes them very desirable items.

    I admire your diligence in tracking down the identity of the Radford amp. Well done!
    Last edited by Barry; 19-04-2021 at 11:51.
    Barry

  4. #14
    Join Date: Sep 2014

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    I'm John.

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    I’m sure there’s been some water under the bridge since the article was written Barry

  5. #15
    Join Date: Feb 2013

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    I'm Grant.

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    Quote Originally Posted by barry View Post
    oh - this is embarrassing!

    the table you show is exactly the same as the one shown in our article, there is thus no excuse for me not knowing about it. So definitely a k25, which if the frequency equalisation can be switched out, makes them very desirable items.

    I admire your diligence in tracking down the identity of the radford amp. Well done!
    was a long time ago so i wouldnt worry.. I often forget stuff same day i did it lol
    Regards,
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  6. #16
    Join Date: Jan 2009

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    Thanks Guys, however I do pride myself in having an encyclopeadic knowledge about certain audio brands. Anyway, there was no excuse for me not having carefully read the article I co-wrote.

    Returning to the eBay sale, £2,500 would IMO seem to be a bit of a bargain for the Radford system.
    Barry

  7. #17
    Join Date: Sep 2014

    Location: Northern Ireland

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    I'm John.

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    Barry, it gets worse , have a look at post #16

    https://theartofsound.net/forum/show...s-1960-s/page2

    Looks like the amplifier output impedance is 25 ohm but maybe it’s a multi tap transformer.

  8. #18
    Join Date: Jan 2009

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    The BBC had a habit of taking comercially manufactured items and custom modifying them (or having the manufacturer do it) for their purposes. They did this with Leak, Quad and Radford amplifiers, and with turntables by Garrard, Technics and EMT.

    All of these items were given BBC designations; AM_/_ for amplifiers, and RP_/_ for turntables.

    Ferrograph were another British company who would supply many specialised/customised versions of their reel-to-reel recorders. These would have been variously for the BBC, the Admiralty, and the secret services and GCHQ.
    Barry

  9. #19
    Join Date: Jan 2022

    Location: Sunbury on Thames, UK

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    I'm Florin.

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    Got a pair of Radford Monitor speakers a few weeks back - https://www.radiomuseum.org/r/radford_monitor.html

    It's a 3 way sealed box design:
    - Kef B139 most probably the MKII - 6171 version (rated 40W in closed box),
    - Goodmans mid rage driver,
    - Celestion HF 1300 tweeter.

    Frequency range is quite limited at 45Hz - 15.5kHz

    1. Has anyone attempted to modify the crossover and add a Coles 4001G super-tweeter in order to extend the high range beyond 20kHz? Would it be a complicated procedure for a novice?

    2. Would it be a good idea to upgrade the KEF - B139 6171 (40w) to one of their more recent 1044SP versions (100W)
    Apart from wattage the only other differences other than the size (6171 > 1044) seems to be the Fundamental Resonance (FS) which is 20 for the 6171 and 25 for the 1044SP. Does it matter, would it affect the overall sound signature?!?
    I've calculated the enclosure volume and it's about 50L. The 1044SP radiomuseum.com page here says 1044SP is recommended for cabinets 40 - 60L in volume.

    3. And lastly, I've checked the capacitors inside. There are 4 caps labeled 8uf that score between 13.5 - 16uf, and 2 caps labeled 4uf that score aruond 12uf on the multimeter. There is another one of 0.47 uf that measures 0.49. I'm guessing the last one is fine but the rest of them are way out of their range. Where do I buy replacements if I'm in the UK?

  10. #20
    Join Date: Apr 2012

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    I'm Geoff.

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    That's a nice enough combination of drive units.

    The HF1300 tweeter cuts off rapidly above 13kHz and a Coles supertweeter can be added on a separate filter without modifying the existing crossover.

    If you are over the age of 45, aiming to extend the frequency range up to or beyond 20kHz is likely to be of limited value.

    I doubt you'd gain any benefit from changing the B139.

    The capacitors are probably in need of replacement, there are so many choices it would be best to look for what meets your needs.

    The rear connection terminals are horrible and could be usefully upgraded.

    If it was me, I'd just change the caps and terminals in order to retain a fair degree of originality on what is a collectible speaker.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

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